This longitudinal study will investigate condom use among members of three emerging high-risk groups for STDs and AIDS: adolescents, prostitutes, and heterosexual adults with multiple sexual partners. Subjects will be clients of the King County Sexually Transmitted Disease Clinic and Jail Health Services. Guided by Fishbein and Ajzen's Theory of Reasoned Action model, the specific outcome and normative beliefs associated with condom use, attitudes and norms toward using condoms, and intention to use condoms will be measured. Several extra-attitudinal predictors that may contribute independently to condom use, including prior condom use, perceived control, and drug and alcohol use, will also be measured. The beliefs underlying intention to use condoms will be examined and compared across groups, and within-group sex, age, and ethnicity comparisons will also be made. The ability of beliefs, attitudes and norms to predict intention for each group will be compared. We will compare the standard Fishbein model with an expanded model including extra-attitudinal predictors, using structural equation modeling techniques. We will also compare beliefs and attitudes toward using condoms with new vs. steady sexual partners. A second questionnaire will be administered to the same subjects three months later. This questionnaire will reassess the variables measured at time 1, and will also ask about use of condoms in the preceding three months. The ability of the set of attitudinal and intention variables to predict subsequent behavior will be tested, and comparisons made between the standard model and the expanded model including extra-attitudinal predictors, across risk groups and across sub-groups within risk groups, and for use with new vs. steady sexual partners, as above. We will also be able to compare this time 2 data with time 1 data and track changes in specific beliefs and attitudes in these high risk groups over time. The findings of this study should suggest specific attitude-change interventions that will lead to increased condom use among members of these high-risk groups. Tests of the standard vs. expanded Fishbein model will also benefit STD and AIDS research, as well as research on other behaviorally-controlled threats to health, by contributing to the development of a promising model of decision-making.